Thermal conductive liquid display system

ABSTRACT

A display apparatus comprises a thermal conductive liquid (46) in a liquid tight encasing (11) which has a transparent window (13). A direct view display panel (12) with a front area for displaying information is arranged inside the liquid tight encasing (11) in a position with respect to the transparent window (13) such that the information is viewable through the transparent window (13). The direct view display panel (12) is submerged in the thermal conductive liquid (46).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is an U.S. national phase application under 35 U.S.C. §371 based upon co-pending International Application No.PCT/EP2013/076995 filed on Dec. 17, 2013. Additionally, this U.S.national phase application claims the benefit of priority of co-pendingInternational Application No. PCT/EP2013/076995 filed on Dec. 17, 2013,European Application No. 12198221.9 filed on Dec. 19, 2012, and EuropeanApplication No. 13152626.1 filed on Jan. 25, 2013. The entiredisclosures of the prior applications are incorporated herein byreference. The international application was published on Jun. 26, 2014under Publication No. WO 2014/095935 A1.

FIELD OF THE INVENTION

The invention relates to a display apparatus, a digital outdooradvertising system which comprises the display apparatus and a passengerinformation system which comprises the display apparatus.

BACKGROUND OF THE INVENTION

US2012/0255721 discloses an outdoor display apparatus which has animproved configuration to effectively prevent deterioration of a panelincluded therein. The outdoor display apparatus includes: a casing bodyhaving an air inlet and an air outlet, first and second display panelmodules in the casing body to display images on front and rear surfacesof the casing body, respectively, transparent members fittedrespectively to the front surface and the rear surface of the casingbody to protect the first and second display panel modules, an airsuction unit which comprises a fan to suction the air into the casingbody through the inlet via an air filter and to discharge the airthrough the outlet, and an air distribution unit to distribute the airdischarged from the air suction unit to at least one of the firstdisplay module and the second display module.

Such an outdoor display apparatus requires regular maintenance becausethe air filters have to be cleaned or replaced and the insidetransparent members have to be cleaned occasionally. The maintenance ofan outdoor display apparatus is very costly. The air space between thetransparent member and the display panel causes poor visibility fromlight reflection and possible contamination by foreign particles andwill reduced the view angle. Further, the fans will consume electricalpower and generate noise. The apparatus will face internal moisturecondensation if the ambient temperature is around zero degrees Celsiusand even frost damage to the display panel glass layers especially ifthe apparatus is not powered at night to save electricity. The apparatusrequires continuous operation or even heating and thus will have a highpower consumption. In public places the transparent members arevulnerable to vandalism, this potential damage risk maybe reduced byincreasing the thickness and laminating the transparent members, theglass will be costly, heavy and will significantly attenuate the lightoutput of the display device so decreases the visibility in daytime. Thewhole construction is quite bulky.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a display apparatus whichhas at least one of the following advantages: the display apparatus doesnot require regular maintenance, has improved visibility under allweather conditions, does not have to be powered 24 hours a day, has norisk for frost damage, has a lower power consumption (is a ‘GreenDesign’), is less vulnerable to vandalism, produces less noise, is lessbulky, has a longer lifespan, has an improved Mean Time Between Failuresand lower Total Cost of Ownership.

A first aspect of the invention provides a display apparatus as claimedin claim 1. A second aspect of the invention provides an outdooradvertising system as claimed in claim 12. A third aspect of theinvention provides a passenger information system (PIDS) comprising thedisplay apparatus as is claimed in claim 13. Advantageous embodimentsare defined in the dependent claims.

A display apparatus in accordance with the first aspect of the inventioncomprises a liquid tight encasing in which a direct view display panelis arranged.

The liquid tight encasing is filled with a thermal conductive liquidsuch that the direct view display panel is submerged in the liquid. Theliquid tight encasing comprises a transparent window to enable aspectator to see a front area of the direct view display panel throughthe transparent window. The front area of the direct view display panelis the area where the information is displayed. The informationdisplayed may be any kind of information to be conveyed to thespectator, for example a static picture, a series of pictures, a movieor any other moving information, text, departure and arrival time ofpublic transportation vehicles, scrolling advertisements, publicaddressed government messages or any combination thereof.

The claimed display apparatus provides at least one of the followingadvantages.

The use of the liquid tight encasing prevents any dust or moisture toenter the system. Moisture will especially occur in colder climates innon-heated housings to save electricity at night, it will corrode theelectric parts and may enter the delicate display glass layers causingfrost fatal cracks and the moisture will appear as fog on thetransparent window making the apparatus useless under thesecircumstances.

The thermal conductive liquid conducts the heat generated by componentspresent in the liquid tight encasing to the wall or walls of the liquidtight encasing which dissipates the heat into the ambient. For example,the thermal conductive liquid may be a mineral oil or silicon oil. Thefan and the air inlet and outlet are superfluous and thus a very compactconstruction may be obtained. In an embodiment, the wall or walls of theliquid tight encasing have a high thermal conductivity. For example,this wall or these walls are made of metal. The wall or walls may haveprotrusions at the inner side (in the thermal conductive liquid) or atthe outer side (for example, in the ambient air) or both to improve theheat transfer from the thermal conductive liquid to the ambient of theliquid tight encasing.

The liquid cooled backlight may run at a much lower temperature than by(forced) air cooling. This lower temperature will boost the lifespan ofthe backlight elements or can be used to increase the backlight currentto achieve higher display brightness without adding backlight elements.

The liquid absorbs impacts, shocks, vibration from outside likevandalism attacks, collisions, and vehicle motion.

The protective transparent window can be thinner or non-laminated andconsequently the brightness and visibility of the displayed informationwill improve at the same power consumption. The transparent window doesnot need an antireflective surface at the inside which produces diffusescattered light and reduces the brightness. The invention will reducethe cost of the window and increase the brightness, visibility further.

The liquid absorbs the UV light from the sun and thus protects andenlarges the lifespan of the display

The liquid effectively transports the absorbed heat from the sun fromthe delicate front side to the cool sides and the back of the apparatus.Without forced air cooling or the new emerged liquid cooling thetemperature in the enclosure may reach 90 degrees Celsius because of agreenhouse effect and self-heating of the electronics causingoverheating and permanent damage to most standard display panel modules.

In an embodiment, the liquid tight encasing is completely filled withthe thermal conductive liquid and does not contain any air. The lack ofair inside the apparatus and the tight enclosure will prevent sparksmaking the product suitable for explosion proof applications likerequired in the oil and gas industry.

In an embodiment of the invention, at least a subset of the electroniccircuits required to operate the direct view display panel is arrangedinside the fluid tight encasing and is submerged in the liquid. Now theliquid is also cooling the submerged electronic circuits. The liquid maybe electrically non-conductive. Alternatively, the electronic circuitsmay be sealed such that the liquid need not be non-conductive. Such asealing should be thermal conductive. The submerging of the electroniccircuits has the advantage that the cooling of the electronic circuitsdoes not need any other cooling system than the already present one forthe direct view display panel. Also for the electronic circuits there isno need to add a fan and air filter.

In an embodiment of the invention relevant for mains operatedapparatuses, the electronic circuits comprise a processing circuit fordriving the direct view display panel and an AC to DC power converterfor converting the AC-mains voltage into power supply voltages for thedisplay processing circuit.

In an embodiment of the invention relevant for battery operatedapparatuses, the electronic circuits comprise a battery, a processingcircuit for driving the direct view apparatus and a DC to DC powerconverter for converting a DC-voltage supplied the battery into powersupply voltages for the processing circuit. Independent on whether theapparatus is mains or battery operated, all the components may besubmerged in the liquid within the liquid tight encasing such that asingle cooling system suffices.

In an embodiment of the invention, the front area of the direct viewdisplay panel is spaced apart from the transparent window for allowingthe liquid to flow between the front area and the transparent window.This allows cooling the display panel also at the front area.

In an embodiment of the invention, a refractive index of the liquid, arefractive index of a material of the transparent window and arefractive index of a transparent material covering the front area ofthe direct view display panel are matched. The matched refractiveindices have the advantage that minimal reflections occur in the opticalpath under all view angles resulting in a high brightness and thusimproved visibility. In a prior art technique the display panel and thetransparent window are bounded with an optical matched permanent glue.This known technique is technically complicated and costly. A furtherdisadvantage of the known technique is that the window and display panelcan never be separated, a broken window always means a broken display.The invention will save the cost of manufacture and the cost ofoperation because the window (and the liquid within) can still bereplaced in the field.

In an embodiment of the invention, the liquid tight encasing comprises aheat sink area for dissipating heat into the ambient of the liquid tightencasing. Such a heat sink area may be integrally formed with a wall ofthe liquid tight encasing or may be a separate heat sink mounted on awall of the liquid tight encasing.

In an embodiment of the invention, a liquid pump may be arranged insidethe liquid tight encasing to improve a liquid flow inside the liquidtight encasing.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIGS. 1A and 1B schematically show a first embodiment in accordance withthe present invention, and

FIG. 2 schematically shows a second embodiment in accordance with thepresent invention.

It should be noted that items which have the same reference numbers indifferent Figures, have the same structural features and the samefunctions, or are the same signals. Where the function and/or structureof such an item has been explained, there is no necessity for repeatedexplanation thereof in the detailed description.

DETAILED DESCRIPTION

FIGS. 1A and 1B schematically show a first embodiment in accordance withthe present invention. FIG. 1A shows a display apparatus 1 with a module45. The display apparatus is of the type suitable for direct view of thepixels of the display panel and is not intended to cover projectionsystems which anyhow are considered too bulky in the context of thepresent invention. The term direct view display panel thereforeindicates that a spectator can directly view the information on thedisplay panel via the transparent window 13.

FIG. 1B shows the module 45 in isolation. The module 45 comprises theliquid tight encasing 11 with the transparent window 13. The liquidtight encasing is filed with a thermal conductive liquid 46. The directview display panel 12 is arranged inside the liquid tight encasing 11and is submerged in the thermal conductive liquid 46. It is notessential for the present invention that the thermal conductive liquid46 is present at all sides of the direct view display panel 12. Thewalls of the liquid tight encasing 11 may be made of metal. Thetransparent window 13 may be made of glass or plastic. The direct viewdisplay panel 12 may use any suitable direct view display technology,such as for example: LCD, TFT, LCM, LED or OLED. If present, thebacklight 17 may be of any suitable type, such as for example: whiteLED's, colored LED's, CCFL lamps, or TL lamps and may be arranged at anysuitable position with respect to the display area, for example at theside, at the corners or at the back of the display panel 12. The displaypanel may be of the reflective or transmissive type, or a combinationthereof.

In FIG. 1A, the module 45 is arranged inside a housing 49 which forexample is a metal shell. The part within the dashed line indicated by 1is referred to as the Electronic Information Display and is in the nowfollowing also referred to by the abbreviation EID. The optional supportstructure 2 may keep the EID in a particular position. The EID may bemoveable into a desired direction at the particular position. The EIDmay be an integral part of another device, for example inside a videocamera or may be carried in a mobile device. The EID may be used insidea building, a shelter, a vehicle on land, sea, under water, in the air,outside the earth atmosphere, or may be hand or cloth carried. Theliquid tight module 45 seals the direct view display panel 12 fromambient influences such as for example moisture (for examplecondensation), frost, dirt, explosive and corrosive materials (forexample: salt water, chemicals, oil, explosive gas).

The electronic processing circuit 14 drives the display panel 12. Theprocessing circuit 14 may be a standard display controller or may be asuitably programmed embedded computer or a combination of both. Thepower converter 15 converts the AC mains voltage, or an external DCvoltage, or a DC voltage of the optional battery 16 into power supplyvoltages required by the processing circuit 14. The external DC voltagemay originate from a vehicle in which the display apparatus is used. Theprocessing circuit 14 may generate the information to be displayed onthe display panel 12 and generates drive signals to drive the displaypanel 12 such that the information is actually displayed. Alternatively,the processing circuit 14 may receive the information to be displayedfrom a remote location, for example by internet or any other wired orwireless communication channel.

The optional heat sink 42 is arranged at the back side of the displayapparatus and may have protrusions to enlarge the cooling area. The heatsink 42 may be attached to other walls of the display apparatus or toall sides of the display apparatus except the display area. The heatsink 42 may be attached to or may be an integral part of the housing 49.Alternatively, the heat sink 42 may be attached to or may be an integralpart of the liquid tight encasing 11. An optional sun shade arrangement43 may prevent the sun to directly shine on the heat sink 42. The sunshade arrangement may only shield a part of heat sink 42. The sun shadearrangement 43 may have ventilation holes. Optionally the sun shadearrangement 43 may have protrusions extending backwards in horizontal orvertical direction or in an array like manner to prevent the sun toshine through the ventilation holes onto the heat sink 42.

In an embodiment, a gap 44 is present between the inner side of thetransparent window 13 and the front side of the display panel 12 suchthat the thermal conductive liquid 46 is present between the transparentwindow 13 and the display panel 12. This allows the thermal conductiveliquid 46 to flow along the front side of the display panel 12 to coolthis front side. The optional heat conductor bridge 48 may be part ofthe housing 49 and has the function to improve the transport of heatfrom the liquid tight encasing 11 to the heat sink 42. In an embodiment,the heat conductor bridge 48 is made of solid metal, for examplealuminum or may be a heat pipe.

Optionally, a fan 20 may be added to cool the heat sink 42. Optionally,a touch screen 21 may be present in front of the window 13 or may beintegrated into the window 13. The touch screen 21 may cover thecomplete window 13 or only a portion thereof.

FIG. 2 schematically shows a second embodiment in accordance with thepresent invention. The items which have identical reference signs to theitems shown in FIGS. 1A and 1B are not discussed anymore. The differencebetween the embodiment shown in FIG. 2 and the embodiment shown in FIGS.1A and 1B is that the housing 49 is now the fluid tight encasing 11. Thethermal conductive liquid 46 now fills the complete housing 49 of FIGS.1A and 1B. Consequently, also the electronic circuits 14, the powerconverter 15 and the optional battery 16 are embedded in the thermalconductive liquid 46. It is not essential for the present invention thatthe battery 16 is embedded in the thermal conductive liquid. The termembedded does not indicate that the item should be surrounded at allsides by the liquid 46. An optional liquid pump 39 may be present toimprove the flow of the thermal conductive liquid 46 inside the fluidtight encasing 11. The pump may be controlled by a thermostatic switchor an electronic temperature control device. The flow of the thermalconductive liquid 46 is indicated by the arrows 48. This flow may beconvection due to the temperature differences in the thermal conductiveliquid. The flow may be enlarged by adding the liquid pump 39.

The present invention provides protection against overheating bydirectly impinging sun light (1000 W per square meter) without requiringexpensive maintenance (cleaning 1 to 2 times a year the air filters).Due to the improved cooling, it is further possible to either obtain alonger lifetime or to increase the backlight power without decreasingthe lifetime.

The present invention may have many applications in systems where adisplay is present, some of which are mentioned in the now following: anoutdoor digital advertising system; a passenger information systemoutdoor or inside a vehicle; an ATM or Kiosk display unit; an outdoormobile display device; a touchscreen of any technology like IR,Resistive, Capacitive; an ultrasound apparatus; any sun or daylightexposed display apparatus; any waterproof display apparatus; anylife-support or medical display apparatus; any Aerospace displayapparatus; any automotive display apparatus; any professional orconsumer AV display apparatus; any military display apparatus; anygeneral transportation, like rail, tram, bus; any indoor application;any marine system; any gaming, casino or entertainment system; any gasstation application; any industrial application; any mobile phone orPDA; any digital signaling system: any Point of sale; any payment cardreader device; any digital shelf advertising system; any transparentscreen comprising the display apparatus; any outdoor monitor systemcomprising the display apparatus as claimed in any one of the precedingclaims. The present invention does not exclude enclosures withadditional fans.

It should be noted that the above-mentioned embodiments illustraterather than limit the invention, and that those skilled in the art willbe able to design many alternative embodiments without departing fromthe scope of the appended claims.

To counteract the volume change of the thermal conductive liquid (forexample: oil) at changing temperature, the material of the cabinet mayhave a compensating temperature coefficient. Alternatively, an expansionvolume may be present. Such an expansion volume may be a gas bubble(like air or nitrogen) inside the enclosure, a gas (for example, air)filed pouch floating in the thermal conductive liquid, or may be avolume filed with a gas, which volume is separated from the thermalconductive liquid by a flexible membrane. Alternatively, a piston may beused instead of the membrane. The expansion volume may be completelyinside or outside the cabinet or may be present partly inside and partlyoutside the cabinet. What is important is that any suitable means arepresent to allow the volume of the thermal conductive liquid to changewith changing temperature. In a practical implementation it appearedsufficient to cover a 2% change of the volume of the thermal conductiveliquid over the operating temperature range. Alternatively the housingcan be (semi) open at the top, (like an aquarium) so the liquid couldexpand into the ambient atmosphere (gas).

The invention also may be used for optical bonding purposes only with anarrow gap 44. The narrow gap 44 may prevent liquid to flow and cool butmay improve the optical performance of an outdoor display such as anoutdoor advertising system and a digital outdoor advertising system.

Dependent on the construction of the display panel and if present it'sbacklighting, care should be taken to liquid tight seal thisconstruction such that the thermal conductive liquid does not alter theoptical behavior of the construction. For example in a constructioncomprising a LCD display panel and a conventional backlighting, thebacklighting should be fluid tight sealed to prevent the thermalconductive liquid to enter between the different elements (for example,the diffuser layers) of the backlighting where the thermal conductiveliquid would cause a change of the optical properties of theconstruction. Alternatively, a dedicated backlighting may be used whichis designed to be filled with the thermal conductive liquid.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. Use of the verb “comprise” and itsconjugations does not exclude the presence of elements or steps otherthan those stated in a claim. The article “a” or “an” preceding anelement does not exclude the presence of a plurality of such elements.The invention may be implemented by means of hardware comprising severaldistinct elements, and by means of a suitably programmed computer. Inthe device claim enumerating several means, several of these means maybe embodied by one and the same item of hardware. The mere fact thatcertain measures are recited in mutually different dependent claims doesnot indicate that a combination of these measures cannot be used toadvantage.

The invention claimed is:
 1. A display system comprising a modulecomprising: a liquid tight encasing being filled with a thermalconductive liquid, said liquid tight encasing comprising a transparentwindow; and a direct view display panel submerged in said liquid, saiddirect view display panel having a front area for displaying informationand being arranged inside said liquid tight encasing in a position withrespect to said transparent window for allowing direct viewing of theinformation through said transparent window; and a housing configured asa shell to fully encapsulate said module therein with sand transparentwindow being in communication with an exterior of said housing.
 2. Thedisplay system as claimed in claim 1 further comprising a backlightarranged inside said liquid tight encasing so as to be cooled by saidliquid, said direct view display panel and said backlight beingsubmerged in said thermal conductive liquid.
 3. The display system asclaimed in claim 2, wherein a refractive index of said thermalconductive liquid, and a refractive index of a material of saidtransparent window are matched.
 4. The display system as claimed inclaim 2 further comprising an embedded temperature control to spread andcontrol trapped ambient heat by circulating said thermal conductiveliquid.
 5. The display system as claimed in claim 4, wherein said frontarea of said direct view display panel is spaced apart from saidtransparent window for allowing said thermal conductive liquid to flowbetween said front area and said transparent window to allow circulationof said thermal conductive liquid and control of the trapped ambientheat.
 6. The display system as claimed in claim 4 further comprising aliquid pump arranged inside said liquid tight encasing and said embeddedtemperature control for obtaining an increased liquid flow of saidthermal conductive liquid inside said liquid tight encasing.
 7. Thedisplay system as claimed in claim 4 further comprising a sun shadeconfigured to prevent light to directly shine on at least a portion ofsaid heat sink of said embedded temperature control.
 8. The displaysystem as claimed in claim 7, wherein said sun shade includesventilation holes defined therethrough.
 9. The display system as claimedin claim 8, wherein said sun shade includes protrusions extendingbackwards therefrom, said protrusions are configured to prevent light toshine through said ventilation holes onto said heat sink.
 10. Thedisplay system as claimed in claim 1 further comprising electroniccircuits for operating said direct view display panel, said electroniccircuits are arranged inside said housing containing said liquid tightencasing.
 11. The display system as claimed in claim 1 furthercomprising a touchscreen adjacent said window exterior or interior ofsaid liquid tight encasing.
 12. The display system as claimed in claim1, wherein a refractive index of said thermal conductive liquid, and arefractive index of a material of said transparent window are matched.13. The display system as claimed in claim 1 further comprising anembedded temperature control to spread and control trapped ambient heatby circulating said thermal conductive liquid.
 14. The display system asclaimed in claim 1 further comprising: electronic circuits for operatingsaid direct view display panel, said electronic circuits having alocation selected from the group consisting of inside said liquid tightencasing and submerged in said thermal conductive liquid, and inside ahousing containing said liquid tight encasing; and a touchscreen havinga location selected from the group consisting of embedded in said liquidtight encasing, and adjacent said window exterior of said liquid tightencasing.
 15. The display system as claimed in claim 10, wherein saidhousing further comprises a heat sink area for dissipating heat into anambient of said housing.
 16. The display system as claimed in claim 15,wherein said housing further comprises at least one heat conductorbridge configured to transport heat from said liquid tight encasing tosaid heat sink.
 17. The display system as claimed in claim 16, whereinsaid electronic circuits are arranged inside said housing between saidliquid tight encasing and said heat sink, and an area of said housingincluding said electronic circuits is in communication with a portion ofsaid heat conductor bridge.
 18. The display system as claimed in claim17, wherein said electronic circuits include a processing circuit, apower converter, and a battery.
 19. The display system as claimed inclaim 17 further comprises a fan located exterior and adjacent said heatsink to cool said heat sink.
 20. The display system as claimed in claim17 further comprises a sun shade located exterior and adjacent said heatsink, said sun shade is configured to prevent light to directly shine onat least a portion of said heat sink.